1. Field of the Invention
The present invention relates to a light source drive which drives a semiconductor laser or so which is a light source used in an optical disk drive or an optical information recording apparatus, such as a CD-R drive, a CD-RW drive, a DVD-R drive, a DVD-RW drive, a DVD+RW drive, a DVD-RAM drive, or so, such an optical information recording apparatus, and an optical information recording method applied therein.
2. Detailed Description of the Related Art
Conventionally, in an optical disk drive, a light source such as a semiconductor laser light source (laser diode or LD) which is a light source is appropriately modulated so as to emit a laser beam, which is applied to an optical information recording medium (optical disk), and thus, information recording and information reproduction are performed thereon. For example, in a phase-change type optical disk used as a CD-RW disk, a DVD+RW disk, etc., an amorphous state, i.e., a recording mark, is formed by increasing the temperature of the recording medium to more than the melting point thereof, and carrying out a sudden cooling thereof so that it is cooled within the crystallization time of the recording medium.
That is, in order to form a properly-shaped record mark and well control the position thereof on the recording medium such as an optical disk, the beam application energy and time duration thereof should be controlled correctly, and it is necessary to generate an exact light waveform in the laser beam. Especially, in case high-speed information writing is required, a control of the characteristic of rising-up and decaying-down of the light waveform is an essential matter.
For example, in a write-once disk employing a pigment such as a CD-R disk, a DVD+R disk, etc., a record mark is formed by producing a thermal deformation occurring from a beam-application or a substrate transformation occurring therefrom so as to cause an optical transformation there.
Accordingly, in order to achieve a proper record mark formation and a position control thereof, it is necessary to generate an exact light waveform in the laser beam applied onto the optical recording medium.
According to Japanese laid-open patent application No. 10-308026, for example, in case of employing a pulse series for driving a laser for well controlling a recording area of an optical recording medium, a snubber circuit is applied so as to absorb a starting power occurring due to a parasitic inductance. Thereby, it is possible to prevent overshooting or ringing otherwise occurring in a laser driving beam waveform due to the parasitic inductance included in a circuit used for transmitting the driving signal up to the laser with high-frequency components included in the pulse series.
With regard to other types of optical recording media such as MO or MD for which a magnetic inversion phenomenon occurring near the Curie point is utilized, the same situation occurs.
In such a conventional light source drive described above, the following problems to be solved are involved. FIG. 1 illustrates the problem occurring in a case of driving an LD (laser diode) in a conventional light source drive. FIG. 2 shows waveforms in case the LD is driven by the light source drive shown in FIG. 1.
In FIG. 1, in order to simplify the description, in an LD drive part 201, illustration is omitted except a source of current which supplies a drive current.
Generally speaking, some amount of junction capacitance occurs between an anode and a cathode of the LD (in addition, a parasitic capacitance also occurs there). In the figure, the reference numeral 203 indicates a simple LD equivalent model in consideration of this junction capacitance.
‘CLD’ in this LD equivalent model 203 indicates the above-mentioned junction capacitance (the above-mentioned parasitic capacitance is also included therein), ‘r’ indicates an ON resistance, and ‘LDi’ indicates an ideal LD. Due to the occurrence of the junction capacitance, even when a predetermined drive current is provided with a sharp rising-up and a sharp decaying-down in its waveform, i.e., of a rectangular waveform, as shown in FIG. 2A, a part of the current is to flow through the junction capacitance as a charging/discharging current Ic therefor. Accordingly, the current then flowing through the ideal LD (LDi) has not sufficiently sharp rising-up and decaying-down, i.e., rounded, as shown in FIG. 2B. As a result, it becomes not possible to drive the LD with a desired signal waveform such as that shown in FIG. 2A.
Thereby, it may not be possible to produce a precisely shaped record mark or a well controlled mark position on a relevant optical recording medium, and, thus, the data recording may include data errors accordingly.
Especially, in case of achieving high-speed recording of information onto an optical recording medium, an output of the LD should be increased accordingly. However, generally speaking, a high-output LD has a large junction capacitance, and, also, in this case, high-speed rising-up and decaying-down of signal waveform is essential. Accordingly, the above-mentioned problem of possible data error generation due to degradation in the signal waveform rising-up and decaying-down performance may become remarkably worse. This problem is referred to as a first problem.
Moreover, generally speaking, a transmission line 202 which provides the drive current from the LD drive part 201 to the LD is installed usually on a flexible printed circuit board (FPC), and in the transmission circuit 202, as shown in FIG. 1, parasitic inductances Lp1 and Lp2 and parasitic capacitances Cp1 and Cp2 may occur.
In case a high-speed modulation or driving of the LD is carried out, the signal of a high-frequency component causes a resonance phenomenon with these parasitic inductances etc. As a result, the drive current includes overshooting or ringing, as shown in FIG. 2C, and then, it may become not possible to achieve generation of a light beam with a desired waveform from the LD. Accordingly, record marks thus formed on the optical recording medium may not have proper shapes nor well-controlled positions, and, thus, as mentioned above, data errors may occur at a time when information reproduction is made from the recording medium. This problem is referred to as a second problem.
The above-mentioned first and second problems may occur simultaneously in combination in some cases.